Diffusional Behavior of Solvents and Amino Acids in Network Polystyrene Gels As Studied by1H Pulsed-Field-Gradient Spin−Echo NMR Method

The diffusion coefficients of N, N -dimethylformamide (DMF) and tetrahydrofuran (THF) in Merrifield network polystyrene gels used as a solid-phase reaction field have been determined as a function of the degree of volume swelling ( Q ) over the temperature range from 30 to 80 °C by means of the 1 H pulsed-field-gradient spin−echo NMR method. From these experimental results, it was found that the D values for DMF in network polystyrene gels linearly increase with an increase of Q in the Q < 3.2 range, and a change of the D value for DMF in the Q > 3.2 range is smaller than that in the Q < 3.2 range. The activation energies of self-diffusion ( E ) for DMF in network polystyrene gels as determined from the temperature dependence of D are linearly decreased with an increase of Q in the Q < 1.8 range, and change of the E value for DMF in the Q > 1.8 range is very small. From these experimental results, it was found that the Q dependence of the D value for THF in network polystyrene gels is very similar to that of DMF. Further, it was found that the D values for DMF in network polystyrene gels with Q < 1.8 were significantly influenced by the fraction of chloromethylation in the phenyl rings of network polystyrene. Further, from the diffusion coefficient measurements of Boc-Gly( tert -butyloxycarbonylglycine) and Boc-Phe( tert -butyloxycarbonyl- l -phenylalanine) in network polystyrene gels, it was found that Boc-Gly and Boc-Phe in network polystyrene gels have multicomponents in diffusion by intermolecular interactions between amino acids and polymer network and that the diffusional behavior of Boc-Gly in network polystyrene gels is very close to that of Boc-Phe.